The basic test for bacterial contamination is Total Coliform Bacteria. Total Coliform is an indicator of the sanitary condition of a water supply. Total Coliform includes bacteria that is found in soil, in water that is on or near the surface of the ground, and in human or animal waste.

When Total Coliform is found in a private well supply, the first step is usually to check the well for any physical defects. A broken or missing well cap, or a well casing which is too close to the surface of the ground or is located beneath the ground, can allow surface water, insects, and debris to enter the well. If any of these conditions are found, they should be corrected and the water should be retested.

A well may prove to be inviting to insects, especially during dry conditions and high temperatures. Sometimes when checking a well, there is evidence that insects are using the well casing for a nesting area. When this is found, the problem can be controlled by covering the top of the well casing with plastic screening and fastening it to the well casing with a large screw clamp. This covering of screening will also prevent small rodents such as mice and moles from entering the well. Mice have been known to squeeze through a space as small as a coin slot. Since one-half inch or more of space is found around the average well casing, mice and other rodents can easily enter. Once they fall into the water, they may be disoriented and not be able to find their way out. Finding rodent hairs in the faucet strainers is one clue that rodents have entered the well.